To come up with their estimates, L&C compares the cost of items you buy in-game to what the similar/comparable items would cost in the real world and uses that to come up with an approximate conversion rate. Then they looked at in-game costs of properties, use their calculated conversion rates, and came up with a rough guide to real-world prices. You can get your real-estate estimates in GBP (£), USD ($), EUR (€), JPY (¥), or AUD (A$).